No vacuum leak, even with the "economy" gage at the 3/4 mark idling in park?


I will check vacuum at 650 RPM.

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'83 240D
'85 300D
'86 300SDL
'88 300E

I'm not sure what it is called by Mercedes. I assume it is not rebuildable, but needs replaced?

AND smoke coming from the intake manifold Rubber boot. Obviously did not tighten that enough when I replaced it?

Gonna pull both to re-seal the boot, and investigate the throttle butterfly.

Is there anything I should be attending to "while I am there"?

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'83 240D
'85 300D
'86 300SDL
'88 300E

Try and think about it like this: you run you vacuum cleaner at full power, great suction. If your vacuum motor were to run at 30% less speed, you would get 30% less suction.

I'm not saying that it's impossible that you have a leak, but your low numbers might be a symptom of your low idle.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

That makes sense and I see your point... I was coming at it from the perspective that my low idle speed was due to the vacuum leak...

I got out the multi meter and took some reading from x11. First readings were 4.2-4.7 Volts =70-65% if my math is correct, and suggesting a lean mix. I got it to the point where it is 5.8-6.2V, 12.5" vacuum, and 700RPM

My question is: at 2500RPM the mixture goes to 8.4-9.5V 39-30%. Well outside the 10% window. Does that mean that my EHA is faulty? Is adjusting it an option?

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'83 240D
'85 300D
'86 300SDL
'88 300E

Should be ticking over with nothing on the economy gauge,in park .So you do have a problem some place .

Hey, (OP) what ever happened?

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

John i dont know .But the economy pointer should read virtualy nothing on tick over and bang over to the left . Check vacuum pipe on the gearbox for a leak . I would eliminate all vacuum and to do this block it off at the source as it comes from ewngine and try again.

I was just reading this thread as I am chasing the same problem on a 1990 300SEL with 313,000 miles.

I noticed that blue85 mentioned an improvement in how the car ran when he had the OVP disconnected, but that was not discussed further. Mine exhibits the same behavior. Slightly low rough idle but when I pull the fuse on the OVP the idle is much stronger and dead smooth.

I think I can rule out ignition and fuel system and focus on sensor input. I'd appreciate anyone's thoughts on that theory.

Thanks,
Kurt

Sounds like you probably have a bad or failing OVP/OVR relay... replace it now if it hasn't been replaced semi recently. They go bad very regularly it seems, especially the aftermarket ones. The cause is corrosion inside the relay due to shoddy weather sealing of the unit (moisture ingress). I've seen it more times than I can remember.

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

I should have mentioned that I had recently replaced the OVP with a Mercedes part. The old one had and bad fuse holder. I did run some Seafoam in the tank and that definitely helped. I only have 60K miles on this set of injectors but the fuel distributor has never been touched since the car was new.
I also tested the throttle switches and both coolant and air temp sensors. The only anomaly was the coolant temp sensor was out of tolerance on the hot side (low resistance) so I ordered a new one. The air temp sensor was just barely within acceptable tolerances but it was reading on the hot side as well so I decided to install a new one.
If any of that helps I'll pass on my results.

Thanks for the feedback.

Kurt

Vacuum Fittings Manufacturer

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Vacuum Fittings,KF Flanges and Fittings,ISO Flange and Fittings,CF Flanges and Fittings
Website:www.rubyvac.com

This morning I changed out the 4-pin coolant temp sensor. When I got the old one out I discovered that the connector housing was split all the way down to the metal part of the sensor and was loose. The plastic was also very brittle. After installing the new sensor the car ran great although the idle is still a little low between 550 and 600 in gear but it is a lot smoother.

I am learning that a lot of little things can contribute to CIS cars idling rough. So far things I have done that have contributed to a nice idle include:

Repairing leaks in rubber hoses and tubing
Replacing rubber fittings and plastic check valves
Achieving maximum pressure difference between upper and lower chambers with EHA adjustment
Adjusting the duty cycle to average about 40%
Replacing old sensors that are on the edge or just our of tolerance

It's a process but very rewarding when you get it right.

I did tell you about this in post 22 . But i still think if your econo guage is not sitting right over to the left or very close to it that you still have vacuum problem some place .You will get there i can tell .Good luck Motorthead .

Optimus,

Looking back you sure did! And after rereading some of your other posts I will pay close attention to the economy gauge when I start the car. I also got my new intake air temp sensor so I will install it tomorrow.

Have you ever tested the altitude correction capsule? I haven't looked at mine yet but did postulate that, if this sensor told the ECU the altitude was high, there would be another correction factor. I live close to sea level so I would expect to see that reflected in the sensor.

Worth checking if you can find it . I no nothing about this sensor so you can teach me on this one .I will keep looking in on this .